In this article, I present a neo-Confucian answer, by Cheng Hao and Cheng Yi, to the question, "Why should I be moral?" I argue that this answer is better than some representative answers in the Western philosophical tradition. According to the Chengs, one should be moral because it is a joy to perform moral actions. Sometimes one finds it a pain, instead of a joy, to perform moral actions only because one lacks the necessary genuine moral knowledge—knowledge that is accessible to every common person as long as one makes the effort to learn. One should make the effort to learn such knowledge—to seek joy in performing moral actions—because to be moral is a distinguishing mark of being human. This neo-Confucian answer seems to be egoistic, as its conception of motivation for morality is based on self-interest: to seek one's own joy. However, since it emphasizes that one's true self-interest is to seek joy in things uniquely human, which is to be moral, self-interest and morality become identical; the more a person seeks one's self-interest, the more moral the person is, and vice versa